Electricity storage device

Abstract

An electricity storage device includes a negative electrode having a layered structure that includes an organic backbone layer containing an aromatic compound having an aromatic ring structure, the aromatic compound being in the form of dicarboxylate anions, and an alkali metal element layer containing an alkali metal element coordinated with oxygen in the dicarboxylate anions to form a backbone, a positive electrode that provides electric double-layer capacity, and a nonaqueous electrolyte solution provided between the negative electrode and the positive electrode, the nonaqueous electrolyte solution containing an alkali metal salt. The layered structure may be provided in layers by a π-electron interaction of the aromatic compound and may have a monoclinic crystal structure belonging to the space group P21/c. The positive electrode may contain activated carbon having a specific surface area of 1,000 m2/g or more.

The invention claimed is: 
     
       1. An electricity storage device comprising:
 a negative electrode having a layered structure comprising multiple organic backbone layers and multiple alkali metal element layers repeatedly, the organic backbone layers containing an aromatic compound having an aromatic ring structure without a carbonyl group, the aromatic compound being in the form of dicarboxylate anions, and the alkali metal element layers containing an alkali metal element coordinated with oxygen in the dicarboxylate anions to form a backbone; 
 a positive electrode that provides electric double-layer capacity; and 
 a nonaqueous electrolyte solution provided between the negative electrode and the positive electrode, the nonaqueous electrolyte solution containing an alkali metal salt, 
 wherein the aromatic compound includes one or more structures selected from the group consisting of structures represented by formulae (3) to (5): 
 
       
         
           
           
               
               
           
         
         where n is an integer of 1 or more and 5 or less, m is an integer of 0 or more and 3 or less, and the aromatic compound has a substituent or a heteroatom in its structure, 
         an area density of the layered structure is 4 mg/cm 2  or more and 8 mg/cm 2  or less, 
         the layered structure includes lithium 2,6-naphthalenedicarboxylate, 
         the positive electrode contains activated carbon having a specific surface area of 1,000 m 2 /g or more, 
         a capacity ratio (B/A) of electric capacity B (mAh) of the negative electrode to electric capacity A (mAh) of the positive electrode is 6 or more, 
         the negative electrode includes a negative electrode mixture containing 2% or more by mass and 8% or less by mass of a water-soluble polymer that is at least one of carboxymethyl cellulose and poly(vinyl alcohol), and 
         the negative electrode includes a negative electrode mixture containing 8% or less by mass of a styrene-butadiene copolymer. 
       
     
     
       2. The electricity storage device according to  claim 1 , wherein the layered structure is provided in layers by a π-electron interaction of the aromatic compound and has a monoclinic crystal structure belonging to space group P2 1 /c. 
     
     
       3. The electricity storage device according to  claim 1 , wherein the layered structure has a structure in which the alkali metal element is tetracoordinated with four oxygen atoms of different dicarboxylate anions, the structure being represented by formula (1): 
       
         
           
           
               
               
           
         
         where each R represents a structure having one or more aromatic rings, two or more of R may be identical, one or more of R may be different, and A represents an alkali metal. 
       
     
     
       4. The electricity storage device according to  claim 1 , wherein the electricity storage device is formed by pre-doping the negative electrode with an alkali metal ion. 
     
     
       5. The electricity storage device according to  claim 1 , wherein the specific surface area of the activated carbon is 2,000 m 2 /g or more. 
     
     
       6. The electricity storage device according to  claim 1 , wherein the negative electrode includes a negative electrode mixture containing 5% or more by mass and 15% or less by mass of a conductive material. 
     
     
       7. The electricity storage device according to  claim 1 , wherein, in the layered structure, each pair of adjacent organic backbone layers of the organic backbone layers are interposed with a respective alkali metal element layer of the alkali metal element layers disposed between the respective pair of adjacent organic backbone layers. 
     
     
       8. The electricity storage device according to  claim 1 , wherein the negative electrode having the layered structure consists of the multiple organic backbone layers and multiple alkali metal element layers repeatedly. 
     
     
       9. The electricity storage device according to  claim 1 , wherein a change in an internal resistance of the negative electrode including the layered structure including lithium 2,6-naphthalenedicarboxylate at a normalized capacity in a range of 0 to −0.1 is higher than a change in an internal resistance of a graphite negative electrode at a normalized capacity in a range of 0 to −0.1. 
     
     
       10. The electricity storage device according to  claim 1 , wherein a calorific value of the electricity storage device comprising the negative electrode including the layered structure including lithium 2,6-naphthalenedicarboxylate is smaller than a calorific value of a electricity storage device including a graphite negative electrode. 
     
     
       11. The electricity storage device according to  claim 10 , wherein the calorific value of the electricity storage device comprising the negative electrode including the layered structure including lithium 2,6-naphthalenedicarboxylate is less than 50% of the calorific value of the electricity storage device including a graphite negative electrode. 
     
     
       12. The electricity storage device according to  claim 1 , wherein a capacity the electricity storage device comprising the negative electrode including the layered structure including lithium 2,6-naphthalenedicarboxylate is higher than a capacity of a electricity storage device including a graphite negative electrode.